Every year thousands of people die while waiting for an organ transplant. Scientists hope that cross-species transplants between humans and pigs will help alleviate part of the shortage. But many questions remain.
These little piglets could grow up to produce human hearts, livers and kidneys.
The statistics are alarming. In 2001, some 14,000 Germans were on the waiting list for organ transplants. Only 4,000 actually took place. Approximately 3,000 people died while waiting for an appropriate donor. The rest are still waiting, buying their time and hoping.
According to the German Society for Organ Transplants, the country requires a yearly availability of 4,500 kidneys, 1,100 livers, and 900 hearts. Not even half of that need is being met with the current donor methods which include both post-mortem and living organ donations.
The situation is similar in other countries in Europe and the industrialized world. The chronic health problems resulting from poor nutrition, smoking, and alcohol lead to a higher demand for replacement organs. However, these newer, healthier organs are not readily available – at least not from humans.
Five cloned piglets were genetically engineered to make their organs more suitable for human transplants.
In animals we trust
In order to meet the growing need for more organ transplants, doctors and medical researchers are turning their attention to pigs. These animals, whose organs are roughly the same size as those of humans, could help alleviate part of the acute demand for kidneys, livers and hearts.
Cross-species transplants or xenotransplantation (xeno = foreign), however is not entirely without biological and ethical questions. A symposium held at the Robert Koch Institute in Berlin this week addressed some of the concerns involved in taking an animal organ and transplanting it into a human.
First, there is the medical-biological aspect. Are the animal organs fully compatible with human physiology?
Studies in the past have shown that animal-to-animal transplants, for instance between a monkey and a pig, can be successful. Once inserted into the foreign animal, the organs need time to adjust to the new physiological environment, but the incidence of organ rejection is not much higher than within same species transplants.
Introducing an animal’s kidney into a human organ system, however, is something entirely different, say scientists. In particular, there is an increased level of disease transfer possible.
Pigs, the most likely source for human xenotransplantation, carry viruses not ordinarily found in the human population. And these can be easily transferred by the import of a pig organ. The result could be the spread of a contagious disease among the humans.
Scientists say there is no way to completely rule out such a possibility. Only a series of studies presented at the Robert Koch symposium by American and European scientists show that the chance of this happening is fairly slight. The so-called procinen endogenen retroviruses (pig viruses) are linked to the genetic make up of the pig and would therefore have little effect on humans.
Among the 160 patients worldwide who have received animal organ or cell transplants, there has been no incidence of a disease being passed from one species to the other.
Nonetheless, not everyone is convinced of the biological compatibility of xenotransplantations. The studies only show that the scientific community is one step closer to carrying out such organ transplants. It will still be quite some time before the medical community, doctors and hospitals, begin carrying out pig-to-human transplants.
Science still leaves many questions unanswered
Although scientific studies may help to answer many of the biological questions, there are still several ethical issues that need to be addressed before xenotransplantation is openly embraced as a solution for the organ shortage.
Is it ethical to "harvest" animal organs and to raise animals specifically for the therapeutic properties of their lungs, livers and kidneys? In Germany, where animal rights are now guaranteed by the country’s constitution, the ethical dilemma becomes especially tricky.
By slaughtering an animal for the purpose of keeping a human alive, one effectively says that the needs of humans are above those of animals. In a sense then, xenotransplantation establishes a hierarchy in which animals exist to serve humans. Of course, avid vegetarians would argue that this is only a continuation of the current practice of raising and slaughtering pigs, cows and chickens to feed the human population.
Another question, is of course the mixing of species. Many people, including scientists and doctors, ask themselves if it is morally and ethically right to cross the species by transplanting organs. Like a number of people in the population, they shirk at the idea of healing a human with a pig heart and a monkey’s liver. It has something Frankensteiny about it.
A temporary solution
Reinhard Kurth, president of the Robert Koch Institute and organizer of the xenotransplantation symposium in Berlin, cautioned fellow scientists about being overly optimistic. Cross-species transplants are not the cure-all many would like them to be. True, they will help alleviate the organ donor shortage by enabling many people to receive a healthy kidney, heart or liver. But, Kurth warned, no one can know for certain what the long-term consequences of such a transplant are.
Xenotransplantation should remain a temporary solution, Kruth said at the conclusion of the symposium on Friday. According to him, the future of organ transplants lies in the field of stem cell research. Only through the selection and raising of human stem cells, will scientists be able to "create" enough organs and cells to meet the growing demand and at the same time guarantee a high level of biological compatibility.